If you have some free time, let's say in a bus, just a few minutes before the bus arrives to a destination, would you play Grand Theft Auto or Dead Trigger? Would you play any challenging "campaing" games while in a bus? I don't think so.
In this situation, this category of games is probably the best for you. Minimalistic games. One simple objective, simple interface, no thing such as campaing mode or story. Let's see the list. I hope you enjoy it.
7x7 is an awesome minimalistic puzzle game where you have to connect 5 or more blocks with same color.
The game has an awesome interface, no time and it's simple. Also very addictive.
Another awesome game called Strata has been nominated for most innovative game design. You'll know why, when you open it. Awesome design, fancy animations, beautiful interface. This is one of the best games I've ever played. The goal of Strata is to strategically layer colored ribbons to match a pattern. Using forethought and strategy you must sequence your moves correctly. Over time patterns emerge and your tactics may evolve, but Strata will keep you on your toes with increasingly difficult puzzles. A must-have for me.
If you download the Super Hexagon for the first time, you will probably freak out and close the game immediately. However, it will get better for the second time, and soon you will get addicted to the game.
Minimalistic games have to be addictive, and I can assure you, this is one of the most addictive games ever.
Also one of the hardest ones.
To be exact, Auralux is a strategy. A "Music Strategy", maybe. You goal is to occupy all the planets and defend yours. Every second a new warrior is created. If you own two planets, you will recieve two warriors at a time. You can also upgrade the planets to generate more. It's also highly addictive.
As the name says, Dots is a game about connecting...dots. Again, it's a beautiful - connecting, logic and minimalistic game, where your goal is to connect as much dots as possible and gain the highest score. Game has a few modes available, included time-mode.